Yes, we have had a discussion about the LXX before. Fausset makes some good points, and the Alexandrian school may have had some squirrelly ideas.
I can demonstrate, however, that your belief that Massoretic Text based bibles are always right contradicts itself. All you have to do is identify which verse below is the word of God as penned by Solomon. One comes from the Masoretic Text, the other from the LXX. I'm not trying to get one over on you. I'm just trying to point out that we can't always assume the Masoretic text is right.
I never said the Massoretic texts were absolutely perfect either. It has some problems just as all texts do.
Don't you think that's why God gave us so much interconnectedness 'throughout' all Scripture as a whole, repeating relevant subject matter more than once?
That's why the great valley of Zech.14 per the Masoretic text is not a stand-alone idea,
Isa 64:1-3
1 Oh that Thou wouldest rend the heavens, that Thou wouldest come down, that the mountains might flow down at Thy presence,
2 As when the melting fire burneth, the fire causeth the waters to boil, to make Thy name known to Thine adversaries, that the nations may tremble at Thy presence!
3 When Thou didst terrible things which we looked not for, Thou camest down, the mountains flowed down at Thy presence.
(KJV)
Micah 1:3-4
3 For, behold, the LORD cometh forth out of His place, and will come down, and tread upon the high places of the earth.
4 And the mountains shall be molten under Him, and the valleys shall be cleft, as wax before the fire, and as the waters that are poured down a steep place.
(KJV)
Nahum 1:5-8
5 The mountains quake at Him, and the hills melt, and the earth is burned at His presence, yea, the world, and all that dwell therein.
6 Who can stand before His indignation? and who can abide in the fierceness of His anger? His fury is poured out like fire, and the rocks are thrown down by Him.
7 The LORD is good, a strong hold in the day of trouble; and He knoweth them that trust in Him.
8 But with an overrunning flood He will make an utter end of the place thereof, and darkness shall pursue His enemies.
(KJV)
Hab 3:6
6 He stood, and measured the earth: He beheld, and drove asunder the nations; and the everlasting mountains were scattered, the perpetual hills did bow: His ways are everlasting.
(KJV)
Zech 4:7
7 Who art thou, O great mountain? before Zerubbabel thou shalt become a plain: and he shall bring forth the headstone thereof with shoutings, crying, Grace, grace unto it.
(KJV)
Joel 3:11-15
11 Assemble yourselves, and come, all ye heathen, and gather yourselves together round about: thither cause Thy mighty ones to come down, O LORD.
12 Let the heathen be wakened, and come up to the valley of Jehoshaphat: for there will I sit to judge all the heathen round about.
13 Put ye in the sickle, for the harvest is ripe: come, get you down; for the press is full, the fats overflow; for their wickedness is great.
14 Multitudes, multitudes in the valley of decision: for the day of the LORD is near in the valley of decision.
15 The sun and the moon shall be darkened, and the stars shall withdraw their shining.
(KJV)
The forming of that great valley at the Mount of Olives upon Christ's return is also part of the establishing of God's House in Jerusalem for Christ's future thousand years reign (per Ezekiel 40-47).
